The criteria for deciding if an idea has merit as a scientific theory was given previously. Using these criteria one can decide if any particular idea has merit as a scientific theory. It is often the case that more than one idea will have merit as a scientific theory about a given observation. It then becomes necessary to have a way to determine the best theory out of the alternatives.
This is an area of investigation in philosophy related to the kind of logic presented in the last section, but fundamentally different. In the last section the goal was to prove something to be true. In this case the goal is to decide which of competing alternatives is the best one. In the end it is hoped that the one that is determined to be "best" is the one that is true, but the logic will not confirm that. Charles Sanders Peirce considered this question in some detail in the early 1900s. He made the following statement to suggest that scientists must have an effective way of distinguishing between alternatives. This quote of Peirce was taken from an article by Michael Hoffman called Is there a "logic" of Abduction? (http://user.uni-frankfurt.de/~wirth/texte/hoffmann.html). Note: my original link, which no longer works, was http://www.uni-bielefeld.de/idm/personen/mhoffman/papers/abduction-logic.html. The reference is provided for documentation only. It isn't necessary to understand this somewhat technical paper.
| "Consider the multitude of theories that might have been suggested. A physicist comes across some new phenomenon in his laboratory. How does he know but the conjunctions of the planets have something to do with it or that it is not perhaps because the dowager empress of China has at that same time a year ago chanced to pronounce some word of mystical power or some invisible jinnee may be present. Think of what trillions of trillions of hypotheses might be made of which one only is true; and yet after two or three or at the very most a dozen guesses, the physicist hits pretty nearly on the correct hypothesis. By chance he would not have been likely to do so in the whole time that has elapsed since the earth was solidified" (Peirce, 1903:CP 5.172). |
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What is the magic process used by the physicist? I believe it is embodied in a process called abduction. Consider another quote from Peirce (from the same article as before).
| " ... there are but three elementary kinds of reasoning. The first, which I call abduction ... consists in examining a mass of facts and in allowing these facts to suggest a theory. In this way we gain new ideas; but there is no force in the reasoning. The second kind of reasoning is deduction, or necessary reasoning. It is applicable only to an ideal state of things, or to a state of things in so far as it may conform to an ideal. It merely gives a new aspect to the premises. ... The third way of reasoning is induction, or experimental research. Its procedure is this. Abduction having suggested a theory, we employ deduction to deduce from that ideal theory a promiscuous variety of consequences to the effect that if we perform certain acts, we shall find ourselves confronted with certain experiences. We then proceed to try these experiments, and if the predictions of the theory are verified, we have a proportionate confidence that the experiments that remain to be tried will confirm the theory. I say that these three are the only elementary modes of reasoning there are" (Peirce, 1905, c.:CP 8.209). |
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The idea of abduction has been clarified a little bit since the time of Peirce. Hoffman (see above) says "... it becomes clear that the constraining character of contexts is essential for the logic of abduction. ... [the] set of contexts [must be] assumed as relevant in a given historical situation." In other words the context (experimental observations) of the situation can give insight into the truthfulness of a theory that describes the situation. The observations can't prove the theory correct, but the more agreement between theory and observations, the more likely the theory is true. Lorenzo Magnani (http://www.bu.edu/wcp/Papers/Scie/ScieMagn.htm) clarifies the distinction between Peirce and Hoffman: "There are two main epistemological meanings of the word abduction: 1) abduction that only generates plausible hypotheses (selective or creative), and 2) abduction considered as inference to the best explanation, that also evaluates hypotheses." Peirce was working under the first definition while my interpretation of Hoffman fits under the second definition. This course is interested in using abduction in the second sense, to distinguish between alternative theories and arrive at the best one.
Although we will concentrate on the second function in this course, it should be emphasized that abduction is a pattern of reasoning that has two main functions: (a) it is a pattern of reasoning that forces us to come up with alternative explanations for an event of interest; (b) it provides a form or framework for discovering the best explanation, given a set of competing theories (hypotheses) each of which seems to explain an event of interest. The first function is very important, for it is often the case that traditional or habitual or familiar theories are so entrenched and seem so true that there is a tendency to reinterpret the observed event to make it fit the old theories. Phenomena are "perceived" as "already explained" in terms of familiar theories unless an effort is made to look at them in new ways. Abduction requires us to come up with at least one alternative explanation which forces a closer look at the theories and clarifies the thinking involved. In this course the alternative theory will often be provided for you, but it may seem odd or "crazy" because the original theory is so commonly known.
How is it actually done? Consider the conditional statement:
If A, then B.
Consider B to be an initial interesting observation for which we would like to have an explanation and A to be a theory that seems likely to explain B. The conditional might be expressed as "If a certain theory A were true, then it would explain a given interesting observation B."
It is a logical fallacy to infer that A is true because B is known. In other words, you can't conclude A is true just because B is true. This is a well-known error and in fact has a name: fallacy of affirming the consequent. What this shows is that no observation or any set of observations can prove that a theory is true.
However, this doesn't mean that the observations are useless. In fact, a theory must be grounded in observations. How might observations provide credibility for a theory without falling victim to a logical fallacy? Observations can be used, one at a time, to lend support that a particular theory is the correct explanation for the initial observation. To put it the other way around, if a theory leads us to expect relavent observations, there is some credibility to the idea that that theory is the correct one. Observations provide information or data. So, another way of saying the overall principle is "a credible theory gives an explanation for each observation (the data)."
The general procedure is:
Notice that this procedure will not prove A to be the explanation of B, but it will allow determination of the most likely explanation for B out of the alternatives that are provided. Remember that it is the best theory out of the theories being considered. The theory that provides the true explanation may not even be one of the theories being considered!